Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M169/00—Lubricating compositions characterised by containing as components a mixture of at least two types of ingredient selected from base-materials, thickeners or additives, covered by the preceding groups, each of these compounds being essential
  • C10M169/04—Mixtures of base-materials and additives
  • C10M169/041—Mixtures of base-materials and additives the additives being macromolecular compounds only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
  • C23C28/021—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material including at least one metal alloy layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
  • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/02—Couplings; joints
  • E21B17/04—Couplings; joints between rod or the like and bit or between rod and rod or the like
  • E21B17/042—Threaded
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L15/00—Screw-threaded joints; Forms of screw-threads for such joints
  • F16L15/001—Screw-threaded joints; Forms of screw-threads for such joints with conical threads
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L58/00—Protection of pipes or pipe fittings against corrosion or incrustation
  • F16L58/18—Protection of pipes or pipe fittings against corrosion or incrustation specially adapted for pipe fittings
  • F16L58/182—Protection of pipes or pipe fittings against corrosion or incrustation specially adapted for pipe fittings for screw-threaded joints
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2201/00—Inorganic compounds or elements as ingredients in lubricant compositions
  • C10M2201/06—Metal compounds
  • C10M2201/065—Sulfides; Selenides; Tellurides
  • C10M2201/0653—Sulfides; Selenides; Tellurides used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2201/00—Inorganic compounds or elements as ingredients in lubricant compositions
  • C10M2201/06—Metal compounds
  • C10M2201/065—Sulfides; Selenides; Tellurides
  • C10M2201/066—Molybdenum sulfide
  • C10M2201/0663—Molybdenum sulfide used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2201/00—Inorganic compounds or elements as ingredients in lubricant compositions
  • C10M2201/10—Compounds containing silicon
  • C10M2201/102—Silicates
  • C10M2201/103—Clays; Mica; Zeolites
  • C10M2201/1033—Clays; Mica; Zeolites used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
  • C10M2205/18—Natural waxes, e.g. ceresin, ozocerite, bees wax, carnauba; Degras
  • C10M2205/183—Natural waxes, e.g. ceresin, ozocerite, bees wax, carnauba; Degras used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2209/00—Organic macromolecular compounds containing oxygen as ingredients in lubricant compositions
  • C10M2209/006—Organic macromolecular compounds containing oxygen as ingredients in lubricant compositions used as thickening agents
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2215/00—Organic non-macromolecular compounds containing nitrogen as ingredients in lubricant compositions
  • C10M2215/006—Organic non-macromolecular compounds containing nitrogen as ingredients in lubricant compositions used as thickening agents
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
  • C10N2030/06—Oiliness; Film-strength; Anti-wear; Resistance to extreme pressure
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
  • C10N2030/12—Inhibition of corrosion, e.g. anti-rust agents or anti-corrosives
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2040/00—Specified use or application for which the lubricating composition is intended
  • C10N2040/20—Metal working
  • C10N2040/244—Metal working of specific metals
  • C10N2040/246—Iron or steel
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2050/00—Form in which the lubricant is applied to the material being lubricated
  • C10N2050/023—Multi-layer lubricant coatings
  • C10N2050/025—Multi-layer lubricant coatings in the form of films or sheets

Definitions

• This invention relates to a threaded joint for steel pipes and particularly a threaded joint for use in connecting oil country tubular goods to each other. More particularly, this invention is concerned with surface treatment of such a threaded joint.
• a threaded joint for steel pipes according to the present invention can reliably exhibit excellent galling resistance without application of a compound grease which has been applied to threaded joints when they are used to connect oil country tubular goods and which contains a large amount of harmful heavy metal powder. Accordingly, a threaded joint for steel pipes according to the present invention can avoid the adverse effects on the global environment and the human body caused by the use of compound grease.
• Oil country tubular goods (abbreviated as OCTG) are tubing and casing which are used to excavate oil wells for recovering crude oil or gas oil. They are normally connected to each other using threaded joints. In the past, the depth of oil wells was 2,000 - 3,000 meters, but in recent deep sea oil fields, it may reach 8,000 - 10,000 meters.
• a threaded joint for OCTG In its environment of use, a threaded joint for OCTG is subjected to a load in the form of an axial tensile force caused by the weight of OCTG and joints connected thereto, a combined internal and external pressure, and subterranean heat. Therefore, the threaded joint must maintain an airtight connection without breakage even in such a severe environment.
• a typical threaded joint used for connecting OCTG has a pin-box structure comprising a male thread formed on the outer surface of each end portion (pin) of an oil country tubular good and a female thread formed on the inner surface (box) of a coupling (a threaded connecting member).
• An unthreaded metal-to-metal contact portion is formed on the front-end side of the male thread of the pin and on the inner side of the female thread of the box.
• API the American Petroleum Institute
• API requires a threaded joint for OCTG to have sufficient galling resistance to make it possible to carry out tightening (makeup) and loosening (breakout) ten times for a joint for tubing and three times for a joint for casing without the occurrence of galling (unrepairable severe seizure) while maintaining airtightness.
• compound grease When tightening a threaded joint, in order to increase its galling resistance and airtightness, a viscous liquid lubricant referred to as "compound grease" which contains a large amount of heavy metal powder is applied to the contact surfaces (namely, the threaded portions and the unthreaded metal-to-metal contact portions) of the joint.
• compound grease is specified by API BUL 5 A2.
• Compound grease also has the effect of preventing the surface from rusting.
• a threaded joint For the purpose of increasing the retention of compound grease by a threaded joint and improving the sliding properties of the joint, it has been proposed that the contact surfaces of a threaded joint be subjected to surface treatment selected from nitride treatment, various types of plating such as zinc-based plating and dispersed plating, phosphate chemical conversion treatment, and the like to form one or more layers having increased surface roughness.
• surface treatment selected from nitride treatment, various types of plating such as zinc-based plating and dispersed plating, phosphate chemical conversion treatment, and the like to form one or more layers having increased surface roughness.
• the use of a compound grease has a concern of adverse effects on the environment and the human body, as described below.
• Compound grease contains a large amount of powder of heavy metals such as lead, zinc, and copper in order to provide the grease with sufficient lubricity and corrosion resistance.
• Patent Document 1 discloses a joint for steel pipes having at least three layers formed by surface treatment comprising a lowermost nitrided layer, an intermediate chemical conversion layer formed by manganese phosphating treatment, and an uppermost solid lubricating coating.
• Patent Document 2 discloses a threaded joint for OCTG having a lower plated layer with a soft metal such as Cu, Zn, Sn, or Pb and an upper plated layer with a hard metal such as Cr, Mo, or W
• Patent Document 3 discloses a threaded joint for OCTG having a lower coating layer of a material such as Ni having a melting point higher than the temperature of use of the joint and an upper coating layer of a material such as Sn having a melting point lower than the temperature of use of the joint.
• Patent Document 1 JP H08-105582 Al
• Patent Document 2 JP S60-022695
• Patent Document 3 JP H05- 149486 Al
• Patent Document 1 has the defects that the solid lubricating coating wears off at a relatively early stage due to its poor adhesion to the underlying layer, and that it is difficult to retain the lubricating powder released from the coating when it is worn on the wear surface in order to contribute to lubrication. Accordingly, particularly in the case of OCTG made of a high alloy steel with which galling occurs easily, its galling resistance is not sufficient to prevent galling when tightening and loosening of the joint are repeated.
• Patent Document 2 and Patent Document 3 both relate to multi-layer coating with a soft metal and a hard metal on a threaded joint.
• the threaded joint described in Patent Document 2 is premised on the application of a compound grease in order to ensure that the joint exhibits sufficient galling resistance and airtightness. Accordingly, the adverse effect on the global environment and the human body caused by the use of a compound grease cannot be avoided.
• the threaded joint described in Patent Document 3 can exhibit airtightness by melting of the upper coating layer at the temperature of use, but its effect on galling resistance and rust prevention diminishes as tightening and loosening of the joint are repeated due to depletion of the upper layer.
• a more particular object of the invention is to provide a threaded joint for steel pipes having excellent galling resistance, rust preventing properties, and airtightness whereby it can suppress the formation of rust and maintain excellent galling resistance and airtightness without using a compound grease even when the OCTG to be connected by the joint are made of a high alloy steel and tightening and loosening of the joint are repeated.
• Patent Documents 2 and 3 which are not premised on the formation of a solid lubricating coating, there is no disclosure whatsoever concerning a structure which can realize high galling resistance premised on the use of a solid lubricating coating.
• a combination of two undercoat layers namely, a first layer of a relatively hard metal or alloy formed on the steel base metal surface and a second layer of a relatively soft metal or alloy formed on the first layer and beneath the solid lubricating coating is effective at increasing the adhesion of the surface treatment layers to the base metal surface.
• the present invention is a threaded joint for steel pipes constituted by a pin and a box each having a threaded portion and an unthreaded metal-to-metal contact portion serving as contact surfaces of the joint when tightened, characterized in that the contact surfaces of at least one of the pin and the box are coated with a multilayer structure comprising, from the bottom, a first layer formed from a first metal or alloy, a second layer formed from a second metal or alloy which is softer than the first metal or alloy, and a solid lubricating coating as an uppermost layer.
• the threaded joint for a steel plate pipe has at least one of the following features:
• the first layer has a hardness in the range of Hv 100 - 500
• the second layer has a hardness in the range of Hv 10 - 150
• - the second layer has a surface roughness of 1 - 6 micrometers Ra;
• the coating thicknesses of the layers are 2 - 15 micrometers for the first layer, 5 - 30 micrometers for the second layer, and 5 - 40 micrometers for the solid lubricating coating;
• the solid lubricating coating does not substantially contain harmful heavy metals
• the steel pipes contains at least 3 wt% of Cr.
• the contact surfaces of at least one of a pin and a box of a threaded joint which include a threaded portion and an unthreaded metal-to-metal contact portion, are undercoated with two metallic layers having different hardnesses, namely, a first layer of a harder metal or alloy and a second layer of a softer metal or alloy, and then a solid lubricating coating is formed atop these metallic undercoat layers.
• the solid lubricating coating wears at the time of tightening and loosening of the threaded joint.
• wear of the solid lubricating coating causes the lubricant constituent or constituents contained in the coating in powder form to be releases from the coating, and the released powder is embedded in the relatively soft second layer, thereby making it possible to exhibit long-lasting galling resistance.
• the first and second undercoat layers do not melt since the frictional force applied to these layers and hence the frictional heat generated is decreased by the overlaid solid lubricating coating, and they together exert a rust preventing effect on the contact surfaces of the threaded joint.
• a threaded joint for steel pipes according to the present invention can suppress the formation of rust, and it continues to exhibit lubricating performance in the absence of compound grease even when tightening and loosening are repeated and to maintain airtightness after tightening. Accordingly, a threaded joint for steel pipes according to the present invention can maintain excellent galling resistance such that repeated tightening and loosening thereof can be performed without occurrence of galling, and it can prevent galling even when it is a threaded joint for OCTG made of a high alloy steel which is often exposed to a high temperature in a deep oil well or the like or used in a very corrosive environment having a high concentration of hydrogen sulfide.
• Figure 1 shows a steel pipe and a coupling which are assembled for shipment.
• Figure 2 shows the connecting portions of a threaded joint.
• Figure 3 is an explanatory view showing coatings formed on the contact surfaces of a threaded joint according to the present invention.
• Figure 1 schematically shows the assembled structure of a typical threaded joint showing the state of a steel pipe A for an oil country tubular good and a coupling (threaded connecting member) B at the time of shipment.
• a pin 1 having a male threaded portion 3 a on its outer surface is formed on both ends of the steel pipe A, and a box 2 having a female threaded portion 3b on its inner surface is formed on both sides of the coupling B.
• the pin means the element of a threaded joint having a male thread
• the box means the element of a threaded joint having a female thread.
• the coupling B is already connected to one end of the steel pipe A.
• a protector is usually attached to each of the unconnected pin of the steel pipe A and the unconnected box of the coupling B prior to shipment in order to protect the threaded portions of the unconnected pin and box. The protector is removed prior to use of the threaded joint.
• a pin is formed on the outer surface of both ends of a steel pipe and a box is formed on the inner surface of a coupling, which is a separate member.
• a coupling which is a separate member.
• the inner surface of both ends of the steel pipe is made a box and for the outer surface of the coupling to be made a pin.
• Figure 2 schematically shows the structure of a typical threaded joint for steel pipes (also referred to below simply as a "threaded joint").
• the threaded joint is constituted by a pin 1 which is formed on the outer surface of the end portion of a steel pipe A and a box 2 which is formed on the inner surface of a coupling B.
• the pin 1 has a male threaded portion 3 a, an unthreaded metal-to-metal contact portion 4a situated between the threaded portion 3a and the tip of the steel pipe, and a shoulder portion 5 which is an end surface of the steel pipe.
• the box 2 has a female threaded portion 3 b, an unthreaded metal-to-metal contact portion 4b situated on the inner side of the threaded portion 3b, and an innermost shoulder portion.
• the surfaces of the threaded portions 3a and 3b and the unthreaded metal-to- metal contact portions 4a and 4b of the pin 1 and the box 2 form the contact surfaces of the threaded joint. These contact surfaces must exhibit galling resistance and airtightness when the joint is tightened and corrosion resistance. Therefore, a compound grease containing heavy metal powders has conventionally been applied to the contact surfaces. However, as stated previously, the application of a compound grease has adverse effect on the human body and the environment.
• Figure 3 which schematically shows the cross-sectional structure of the coatings formed on the unthreaded metal- to-metal contact portion of a joint
• the contact surfaces of at least one of the pin and the box are coated with a first layer 31 a of a first metal or alloy formed on the surface of steel 30, a second layer 31b formed atop the first layer and made of a second metal or alloy which is softer than the first metal or alloy, and a solid lubricating coating 32 as an uppermost layer.
• the first metal or alloy will be referred to simply as a harder metal
• the second metal or alloy will be referred to simply as a softer metal.
• the solid lubricating coating forming an uppermost layer can exhibit its inherent lubricating properties over a long period due to the underlying two metallic layers having different hardnesses, whereby the threaded joint can be prevented from galling even when it is repeatedly subjected to tightening and loosening and it can maintain airtightness when tightened without using a compound grease.
• the substrate (base metal) for the first layer 31a may be made a rough surface.
• This surface roughening may be achieved by subjecting the surface of the steel 30 to surface roughening treatment such as blasting (including shot blasting and sand blasting) or pickling.
• the first layer 31a made of a harder metal and the second layer 31b made of a softer metal are formed by a suitable method such as electroplating, a suitable surface roughness may sometimes be imparted to the resulting surface of the second layer 31b by shot blasting or sandblasting prior to forming the solid lubricating coating 32 thereon. As a result, the adhesion of the solid lubricating coating 32 is increased.
• the surface treatment to form the above-described three layers according to the present invention may be applied to the contact surfaces of both the pin and the box, but for a pin and a box which are connected to each other at the time of shipment as shown in Figure 1, it is possible to apply the surface treatment to the contact surfaces of only one of the pin and the box.
• surface treatment in order to form the three layers is easier to carry out on a short joint member, so it is convenient to apply the surface treatment to the contact surfaces of a coupling (normally the contact surfaces of the box).
• the first and second undercoat layers and the uppermost solid lubricating coating preferably cover the entirety of the contact surfaces of the pin and/or the box, but the present invention encompasses the case in which only a portion of the contact surfaces (such as only the surface of the unthreaded metal-to-metal contact portion) is coated with the three layers.
• a threaded joint for steel pipes according to the present invention has extremely good galling resistance, so it can prevent galling at the time of repeated tightening and loosening even of a threaded joint made of a high alloy steel which readily undergoes galling. Accordingly, OCTG are preferred as steel pipes which are connected by a threaded joint according to the present invention.
• the type of steel constituting the threaded joint namely, a steel pipe such as an oil country tubular good and a coupling in cases other than an integral joint
• a threaded joint according to the present invention has an undercoat with a two-layer structure consisting of a first or lower layer of a harder metal and a second or upper layer of a softer metal formed on the contact surfaces of a pin and/or a box.
• the metal or alloy used to form the first layer preferably has an Hv hardness of 100 - 500. If it has an Hv hardness of less than 100, its adhesion to the base metal may sometimes be inadequate. On the other hand, if it has an Hv hardness exceeding 500, the resulting coating of the first layer becomes brittle, and it may have a decreased adhesion to the base metal. In addition, cracks tend to easily develop in the coating, leading to a decrease in corrosion resistance.
• the hardness of an electroplated metal coating can be controlled by changing the current density for electroplating, for example.
• the first layer can be formed by a suitable method such as electroplating.
• the coating thickness of the first layer is preferably in the range of 2 - 15 micrometers. If it is less than 2 micrometers, the coating strength decreases to the extent that the first layer may peel easily. If it exceeds 15 micrometers, the first layer may not be able to withstand the shearing force at the time of tightening and may easily peel from the base metal.
• a metal or alloy used to form the second layer preferably has an Hv hardness of 10 - 150 provided that its hardness is lower than that of the first layer.
• the second layer will not have a strength sufficient to support the solid lubricating coating, and even if the lubricating powder released from the solid lubricating coating is embedded in the second layer, the second layer itself may wear away rapidly, thereby making it impossible for the joint to maintain the desired lubricating properties. If the second layer has an Hv hardness exceeding 150, it is too hard to allow the lubricating powder released from the solid lubricating coating to be embedded therein in a sufficient amount, and it becomes difficult for the threaded joint to have long-lasting lubricating properties.
• the second layer can be formed by a suitable method such as electroplating.
• the coating thickness of the second layer is preferably in the range of 5 - 30 micrometers. If it is less than 5 micrometers, the amount of lubricating powder which can be embedded in the second layer may be so small that the galling resistance of the joint becomes inadequate. If it exceeds 30 micrometers, the second layer sometimes cannot support the overlaid solid lubricating coating when a high pressure is applied.
• the surface roughness of the second layer is preferably increased to 1 - 6 micrometers Ra by a known surface roughening treatment such as shot blasting or sandblasting, if necessary. If the second layer has a surface roughness Ra of less than 1 micrometer, the adhesion of the solid lubricating coating to the second layer may become inadequate. If it has an Ra exceeding 6 micrometers, it may become difficult for the softer second layer to have a sufficient coating thickness over its entire surface, thereby decreasing its effect of enabling lubricating powder released from the solid lubricating coating to be embedded therein.
• the first layer and the second layer which are both of metallic nature can be formed by a known plating method such as electroplating, electroless plating, vapor phase plating, or the like. From the viewpoint of economy, electroplating is particularly preferred.
• a thin Ni layer may initially be formed on the surface of the base metal by strike plating in order to improve the adhesion of the first layer, and such a variation is of course encompassed by the present invention.
• Ni strike plating can be performed, for example, using a bath formed by dissolving nickel chloride in deionized water to give a Ni ion concentration of 55 - 80 g/L followed by addition of 30 - 50 g/L of copper sulfate. A commercially available brightener may be added to the bath. A coating thickness of Ni suitable for strike plating can be obtained by plating using this bath at a temperature of 20 - 40° C with a current density of 2 - 6 A/dm 2 .
• the plating conditions may be the same as employed conventionally, and there is no particular restriction thereon.
• the plating conditions for some metals or alloys which can be used to form the second layer will be briefly explained below.
• a Sn plating layer can be formed by electroplating using a plating bath containing, for example, 200 g/L of tin fluoroborate, 125 g/L of fluoroboric acid, 25 g/L of boric acid, 2 g/L of gelatin, and 1 g/L of beta-naphthol at a temperature of 20 - 25° C with a current density of 1 - 5 A/dm 2 .
• a fluoroborate plating bath it is most common to use such a fluoroborate plating bath, but from the standpoint of ease of sewage treatment, it is also possible to use a commercially available, organic sulfonate-based Sn plating bath.
• a Sn-Bi alloy plating layer can be formed in accordance with the alkaline tin plating method or the acidic tin plating method, for example.
• the resulting Sn-Bi alloy plated layer has a hardness which is greatly increased compared to a pure Sn layer.
• the hardness of a Sn-Bi alloy plated layer containing 0.5 - 10% of Bi coprecipitated with Sn is two or three times as high as that of a pure Sn layer (Hv of 8 - 10).
• the plating conditions for the alkaline plating method include, for example, potassium stannate: 100 - 110 g/L, potassium hydroxide: 35 - 60 g/L, Bi: 0.5 - 1.5 g/L as metal, bath temperature: 75 - 85° C, and current density: 0.5 - 3 A/dm 2 .
• the plating conditions for the acid plating method include, for example, organic acid: 130 g/L, Sn: 10 g/L as metal, Bi: 3 g/L as metal, bath temperature: 30 - 40° C, and current density: 0.3 - 3.5 A/dm 2 .
• the plating conditions for Cu-Sn-Bi alloy plating include, for example, organic acid: 130 - 180 g/L, Cu: 1 g/L as metal, Sn: 15 g/L as metal, Bi: 1.5 g/L as metal, bath temperature: 15 - 30° C, and current density: 0.5 - 3.5 A/dm 2 .
• a solid lubricating coating which exhibits a lubricating effect is formed as an uppermost layer atop the above-described two undercoat metallic layers.
• any solid lubricating coating having sufficient lubricity can be used in the present invention as long as it does not have an adverse effect on the environment or the human body.
• a coating has a composition based on a powder having a lubricating activity (referred to below as a "lubricating powder") and a binder and may further contain one or more additives such as a lubricating additive, a corrosion inhibitor, and a pigment.
• lubricating powders include substances which are recognized in the
• OSPAR OSPAR Convention as imposing little or no burden on the ocean environment such as graphite, mica, talc, calcium carbonate, and clay minerals (such as kaolin and bentonite), as well as substances which are known to be nontoxic such as molybdenum disulfide, tungsten disulfide, tin disulfide, PTFE, MCA (melamine cyanurate), gilsonite (natural asphalt), fluorinated graphite, boron nitride (BN), and Bi 2 S 3 .
• a commercially available product can be used for any of these materials.
• the binder may be either organic or inorganic. Namely, it may be an organic resin or an inorganic polymeric compound.
• Organic resins suitable as a binder are those having good heat resistance, moderate to fairly good hardness, and good wear resistance. Examples of such resins include thermosetting resins such as epoxy resins, polyimides, polyamide-imides, polycarbodiimide resins, polyethersulfones, polyether ether ketones, phenolic resins, and furan resins, as well as polyethylene resins and silicone resins.
• these organic resins are formulated into a coating composition by dissolving a resin in a solvent to form a resin solution.
• Various low boiling organic solvents including hydrocarbons (such as toluene) and alcohols (such as isopropyl alcohol) can be used alone or in combination.
• a lubricating powder and optional additives are added to a solution of an organic resin binder to form a coating composition, and the coating composition is applied to the contact surfaces of at least one of a pin and a box which have been undercoated with the first and second layers, thereby forming a solid lubricating coating as an uppermost layer.
• Such post heat treatment is preferably carried out at a temperature of at least 120° C and more preferably at 150 - 380° C for at least 30 minutes and more preferably for 30 - 60 minutes. It is also possible to use a hot melt type binder having a softening temperature in the range of 100 - 220° C, which forms a low viscosity fluid at a high temperature and can be applied without using a solvent. Examples of such a binder include various thermoplastic resins, ethylene vinyl acetate copolymers, polyamides, polyolefin copolymers, and polyurethanes.
• both the base metal having the at least two undercoat layers and the coating composition which is applied and contains lubricating powder are previously heated to at least the softening point of the binder, and the coating composition in which the binder is melted is applied using a spray gun, for example.
• a photo-setting resin can also be used as a binder for a solid lubricating coating. It is usually formulated into a coating composition without using a solvent.
• the inorganic polymeric compound used as a binder for a solid lubricating coating is a compound having a structure formed by three-dimensionally crosslinked metal-oxygen bonds such as Ti-O, Si-O, Zr-O, Mn-O, Ce-O, or Ba-O.
• This compound can be formed by hydrolysis and subsequent condensation of a hydrolyzable organometallic compound, which is typically a metal alkoxide or a hydrolyzable inorganic compound such as titanium tetrachloride.
• Useful metal alkoxides are those having lower alkoxy groups such as methoxy, ethoxy, isopropoxy, propoxy, isobutoxy, butoxy, or tert-butoxy.
• Preferred metal alkoxides are titanium or silicon alkoxides, and titanium alkoxides are particularly preferred. Among these, titanium isopropoxide is most preferred due to its excellent film-forming properties.
• the hydrolyzable organometallic compound used as a raw material for an inorganic polymeric compound may contain a non-hydrolyzable alkyl group which may contain a functional group such as an amine or epoxy group.
• a functional group such as an amine or epoxy group.
• an organometallic compound such as a compound known as a silane coupling agent in which one or two of the four alkoxy groups attached to a silicon atom are replaced by an alkyl group or groups which may contain a functional group can be used as all or a portion of the raw material for the inorganic polymeric compound.
• a coating composition can be formed by adding a lubricating powder to a solution of the metal alkoxide in a solvent and dispersing it therein, and it is applied to the contact surfaces of at least one of a pin and a box which have been undercoated with the first and the second layers.
• a solid lubricating coating having a lubricating powder dispersed in a binder of an inorganic polymeric compound having a structure made of metal-oxygen bonds is formed.
• a solvent for a metal alkoxide various organic solvents including polar solvents such as alcohols (e.g., ethyl alcohol, isopropyl alcohol, butyl alcohol) and ketones, as well as hydrocarbons, halogenated hydrocarbons, and the like can be used.
• polar solvents such as alcohols (e.g., ethyl alcohol, isopropyl alcohol, butyl alcohol) and ketones, as well as hydrocarbons, halogenated hydrocarbons, and the like
• hydrocarbons e.g., ethyl alcohol, isopropyl alcohol, butyl alcohol
• hydrocarbons e.g., halogenated hydrocarbons, and the like
• Humidifying treatment for promoting hydrolysis of the metal alkoxide in the applied coating composition can be carried out by merely leaving the applied surface in air for a certain length of time, but it is preferably carried out in humid air with a relative humidity of at least 70 %.
• heating for curing is carried out after humidifying treatment.
• hydrolysis of the metal alkoxide and condensation of the resulting hydro lyzates as well as discharge of the alcohol produced as a by-product of the hydrolysis reaction are all promoted, leading to completion of film formation in a short period, and the resulting solid lubricating coating has an increased adhesion, which results in an increase in galling resistance.
• This heating is preferably carried out after evaporation of the solvent in the coating composition.
• the heating temperature is in the range of 100 - 200° C and is close to the boiling point of the alcohol which is formed as a by-product. It is still more effective to blow hot air during heating.
• the mass ratio (B/A) of the content (B) of the lubricating powder to the content (A) of the binder in the solid lubricating coating is preferably 0.3 - 9.0. If this mass ratio is less than 0.3, the effect of the lubricating powder on improving the lubricating properties of the solid lubricating coating is not significant, and the joint is not sufficiently improved in galling resistance. If this mass ratio becomes larger than 9.0, the adhesion of the solid lubricating coating decreases significantly, resulting in the occurrence of problems such as separation of the lubricating powder from the solid lubricating coating.
• the above mass ratio is more preferably in the range of 0.5 - 7.0.
• the above mass ratio is still more preferably in the range of 0.5 - 5.0.
• the thickness of the solid lubricating coating is preferably at least 5 micrometers.
• the lubricating powder bound by the binder in the solid lubricating coating is released by the action of the high pressure applied by tightening and spreads over the entire contact surfaces, and some of the released powder is embedded in the underlying second layer made of a softer metal, thereby making it possible to exhibit enduring galling resistance. If the thickness of the solid lubricating coating is less than 5 micrometers, the absolute amount of the lubricating powder contained in the coating becomes so small that the coating may not provide sufficiently improved lubricating properties.
• the thickness of the solid lubricating coating is larger than 40 micrometers, if the thickness of the solid lubricating coating is larger than 40 micrometers. For example, the amount of tightening may become inadequate due to interference between threads, thereby causing a decrease in airtightness, or if the pressure is increased in order to guarantee airtightness, galling may occur easily. In addition, the tendency of the solid lubricating coating to peel increases. However, with some thread geometries, such a thick solid lubricating coating can be used.
• the thickness of the solid lubricating coating is preferably at least 10 micrometers and at most 40 micrometers from the standpoints of decreasing the amount of discharge to the environment as much as possible as well as economy, galling resistance, and rust prevention.
• a coating composition to form a solid lubricating coating can be carried out by suitable known methods such as brush coating, immersion, and air spraying.
• additives including a rust preventing agent can be added to the solid lubricating coating as long as they do not have a significant adverse effect on galling resistance.
• addition of one or more of zinc powder, a chromium pigment, and an alumina pigment can increase the rust preventing properties of the solid lubricating coating itself.
• Additional additives which can be added to the solid lubricating coating include a lubricating additive, an antioxidant, and a coloring agent (pigment).
• a lubricating additive are wax and metal soap such as an alkaline earth metal salt of a fatty acid.
• the wax may be any of animal waxes, vegetable waxes, mineral waxes, and synthetic waxes.
• Waxes which can be used include animal waxes such as beeswax and whale tallow; vegetable waxes such as Japan wax, carnauba wax, candelilla wax, and rice wax; mineral waxes such as paraffin wax, microcrystalline wax, petrolatum, montan wax, ozokerite, and ceresin; and synthetic waxes such as oxide wax, polyethylene wax, Fischer-Tropsch wax, amide wax, and hardened castor oil (castor wax).
• paraffin wax with a molecular weight of 150 - 500 is particularly preferred.
• the alkaline earth metal salt of a fatty acid is preferably an alkaline earth metel salt of a fatty acid having 12 - 30 carbon in terms of the lubricating and rust preventing properties.
• the fatty acid can be either saturated or unsaturated, and it includes mixed fatty acids derived from a natural fatty oil or fat such as beef tallow, lard, wool fat, palm oil, rapeseed oil, and coconut oil, as well as single compounds such as lauric acid, tridecanoic acid, myristic acid, palmitic acid, lanopalmitic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, arachic acid, behenic acid, erucic acid, lignoceric acid, and lanoceric acid.
• the fatty acid salt is preferably in the form of a calcium salt, and it may be either a neutral salt or a basic salt. It is preferably in the form of calcium stearate.
• the contact surfaces of just one (e.g., the box) of a pin and a box of a threaded joint for steel pipes are coated with the multi-layered coating according to the present invention which comprises a first undercoat layer of a harder metal, a second undercoat layer of a softer metal, and an uppermost solid lubricating coating
• the contact surfaces of the other member may remain untreated, but from the standpoint of corrosion prevention, it is preferably coated with either the above- described two undercoat layers or the solid lubricating coating.
• the contact surfaces of the other member may be coated with a rust (corrosion) preventing layer or coating, thereby protecting the surface from air, and even if the surface contacts water which is condensed from the surrounding air during storage of the threaded joint, it is prevented from developing rust.
• a rust preventing coating is broken under the impact of initial tightening of the joint and is united with the solid lubricating coating applied to the other member of the joint to exhibit lubricating properties, so it does not impair lubricating properties.
• the contact surfaces of a pin which includes the surface of its threaded portion and unthreaded metal-to-metal contact portion will be referred to as the "pin surface", and the contact surfaces of a box which includes the surface of its
• the surface roughness is the measured value of Ra unless otherwise indicated.
• the undercoat layers were formed by electroplating, and the solid lubricating coating was formed by air spraying.
• the surface of the second (upper) undercoat layer was roughened by subjecting it to shot blastings lightly. The proportions of the components in each layer are expressed as a mass ratio in the description of each example.
• Galling resistance of a threaded joint was evaluated by the number of tightening cycles before galling occurred in a repeated tightening and loosening test in which tightening was carried out with a tightening speed of 10 rpm and ao tightening torque of 14 kN-m. After loosening of the joint, the state of galling of the contact surfaces of the pin and the box was investigated visually. When the occurrence of only slight galling caused by tightening was observed and it was possible to again tighten the joint after repair, the joint was repaired, and tightening and loosening were continued. The results of the repeated tightening and loosening 5 test are shown in Table 3.
• Cu plating Sn-Bi alloy plating lubricating powder graphite (3 ⁇ m Rmax) 10 ⁇ m thick
• Hy 150 Hy 30 binder hot melt resin (polyamide, thickness: 5 ⁇ m thickness: 12 ⁇ m containing carnauba wax) surface roughness: 2 ⁇ m Ra thickness: 25 ⁇ m
• Example 3 as machined none Ni plating Sn-Zn alloy plating lubricating powder: mica, talc, and B (3 ⁇ m Rmax) Hy 250 Hy 50 bentonite thickness: 5 ⁇ m thickness: 10 ⁇ m binder: polyamide-imide resin O surface roughness: 1.5 ⁇ m Ra thickness: 15 ⁇ m
• the box surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and then coated with a first Cu plating layer with a hardness of
• Hv 200 to a thickness of 4 micrometers by electroplating and then with a second Sn plating layer with a hardness of Hv 10 to a thickness of 5 micrometers also by electroplating.
• the box and pin surfaces of a threaded joint of the 13 Cr steel having composition A shown in Table 1 were subjected to the following surface treatment.
• the box surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and coated initially with Ni strike plating to a thickness of 1 micrometer by electroplating, next with a first Cu plating layer with a hardness of Hv 150 to a thickness of 5 micrometers by electroplating, and then with a second Sn-Bi alloy plating layer with a hardness of Hv 30 to a thickness of 12 micrometers also by electroplating.
• the pin surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and then coated with an acrylic resin to a thickness of 10 micrometers as a rust preventing coating.
• Rmax surface roughness of 3 micrometers Rmax
• acrylic resin to a thickness of 10 micrometers as a rust preventing coating.
• the box surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and then coated with a first Ni plating layer with a hardness of Hv 250 to a thickness of 5 micrometers by electroplating and a second Sn-Zn alloy plating layer with a hardness of Hv 50 to a thickness of 10 micrometers also by electroplating.
• the pin surface remained in an as-machined state (surface roughness of 3 micrometers Rmax).
• the box surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and coated initially with Ni strike plating to a thickness of 1 micrometer by electroplating. Next, it was coated with a first Cu plating layer with a hardness of Hv 250 to a thickness of 8 micrometers by electroplating and then with a second Cu-Sn-Bi alloy plating layer with a hardness of Hv 100 to a thickness of 20 micrometers also by electroplating. The surface of the second plating layer was 5 micrometers Ra.
• the pin surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and then coated with an acrylic resin to a thickness of 15 micrometers as a rust preventing coating.
• Comparative Example 1 The box and pin surfaces of a threaded joint of the 13 Cr steel having composition A shown in Table 1 were subjected to the following surface treatment.
• the pin surface remained in an as-machined state (surface roughness of 3 micrometers Rmax).
• the box surface was finished by machining (to a surface roughness of 3 micrometers Rmax) and then coated with a first Sn plating layer with a hardness of Hv 10 to a thickness of 5 micrometers by electroplating and a second Cu plating layer with a hardness of Hv 150 to a thickness of 10 micrometers also by electroplating.
• the surface roughness of the second plating layer was 1.2 micrometers Ra.
• the same coating layers for the box surface as shown in Table 2 for each example were formed on a separately prepared coupon-shaped test piece (70 mm X 150 mm X 2 mm thick) of the same steel as used in the example, and the coated test piece was subjected to a humidity cabinet test (temperature of 50° C, relative humidity of 98%, duration of 200 hours). From this test, it was ascertained that there was no occurrence of rust for any of the examples.

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